1. Field of the Invention
The present invention relates to a device for controlling the temperature of a semiconductor module and a method of controlling the temperature of a semiconductor module. More particularly, the present invention relates to a device and a method for precisely controlling the temperature of a semiconductor module, which is a test sample on which an environmental temperature test is performed, to a test temperature.
A semiconductor module, such as an optical module having an optical semiconductor element, such as a laser, mounted therein is widely used as a key component of a high-speed communication network as typified by the internet. Among semiconductor modules, the demand for a small coolerless module for intermediate-distance optical communication is increasing.
Such semiconductor modules are often used in locations where high reliability is required of them as in a submarine repeater, or in locations where the temperature environment is severe such as outdoors, so that they are subjected to strict environmental temperature tests to guarantee their reliability.
In environmental temperature tests, the temperatures of semiconductor modules are changed in accordance with a predetermined temperature sequence, during which optical input/output characteristics are observed. Based on the temperature dependencies of the observed semiconductor modules, it is determined whether these observed semiconductor modules are good or defective modules. Therefore, in order to precisely measure the temperature dependencies, it is necessary to precisely control the temperatures of the semiconductor modules.
2. Description of the Related Art
Hitherto, in an environmental temperature test of a semiconductor module, such as an optical module, the temperature of the semiconductor module is kept at the test temperature by placing the semiconductor module on an temperature equalizing block controlled to a test temperature. Hereunder, a related test device will be described.
FIG. 1 is a side view of a related device used for an environmental temperature test of a semiconductor module. Referring to FIG. 1, in the related test device, a heat exchanger 53, a Peltier element 51, and an temperature equalizing block 52 are placed upon each other in that order on a device base 50 in contact with each other. The Peltier element 51 varies the temperature of the temperature equalizing block 52 by absorbing or discharging heat from the temperature equalizing block 52 which is placed in contact with the top surface of the Peltier element 51. The temperature of the temperature equalizing block 52 is detected by a platinum resistance temperature sensor 54 placed inside a hollow near the top surface of the temperature equalizing block 52. The Peltier element is driven so that the detected temperature of the temperature equalizing block 52 is equal to the test temperature, that is, an environmental temperature specified in a test specification.
In a semiconductor module 10, a semiconductor laser element, a built-in Peltier element for controlling the temperature of the semiconductor laser element, and an optical part (none of which are shown) are incorporated in a package 13 including a heat-dissipating plate 12, disposed at the lower portion of the semiconductor module 10, and a cover 11 that covers the heat-dissipating plate 12. In the semiconductor module 10, which is a test sample on which an environmental temperature test is conducted, the bottom surface of the heat-dissipating plate 12 is placed in close contact with the top surface of the temperature equalizing block 52, so that, by conduction of heat from the top surface of the temperature equalizing block 52, the temperature of the semiconductor module 10 is kept equal to the temperature of the temperature equalizing block 52. With the temperatures being kept equal to each other, characteristics of the semiconductor module, such as the light input/output characteristics, are measured.
In the above-described related environmental temperature test device, the temperature of the temperature equalizing block 52 is controlled at a predetermined temperature specified in the test specification. By placing the semiconductor module 10, which is a test sample, on the temperature equalizing block 52, the temperature of the semiconductor module 10 is caused to reach the predetermined temperature of the temperature equalizing block.
However, since the semiconductor module 10 is only placed on the temperature equalizing block 52, heat resistance between the semiconductor module 10 and the temperature equalizing block 52 tends to become large due to contact failure. Considering heat dissipation, the top surface of the semiconductor module 10 (that is, the surface opposite to the surface that contacts the temperature equalizing block 52) is ordinarily designed so that the heat resistance with the ambient atmosphere is small. As a result, a large amount of heat dissipation from the top surface of the semiconductor module 10 causes a large temperature difference to occur due to the heat resistance between the temperature equalizing block 52 and the semiconductor module 10. Therefore, the temperature of the semiconductor module 10 is different by that amount of temperature difference from the predetermined temperature being specified in the test specification. In an ordinary specification of the environmental temperature test, the test temperature is set at the surface temperature of the semiconductor module 10. In such a case, the difference between the temperatures of the temperature equalizing block 52 and the semiconductor module 10 cannot be ignored because it causes a reduction in the accuracy of the test temperature of the environmental temperature test.
To prevent such a temperature difference, an attempt has been made to carry out a method of monitoring the temperature of the semiconductor module 10 using a temperature sensor, such as a thermistor, which is attached to a surface of the semiconductor module 10. However, in this method, the temperature distribution in the semiconductor module varies due to a considerable change in the heat transfer coefficient at the portion to which the temperature sensor is attached, consequently the temperature of the semiconductor module 10 cannot be precisely measured.
In addition, the semiconductor module 10 incorporates elements, including the semiconductor laser element and the Peltier element, which generate or absorb a large amount of heat. The generation and absorption of heat by these elements change the temperature distribution of a portion of the test device that contacts the semiconductor module 10, such as the temperature distribution near the top surface of the temperature equalizing block 52. The temperature sensor 54 of the temperature equalizing block 52 is not necessarily provided at a location where it can precisely detect this temperature distribution. Therefore, it becomes more difficult to precisely measure and control the surface temperature of the semiconductor module.
Another problem with the above-described related environmental temperature test device is that there is difficulty in controlling the temperature of the semiconductor module near room temperature.
Environmental temperature tests usually need to be carried out at ordinary temperatures. This ordinary temperature is generally specified as a temperature near 25 degrees, so that there are cases where there is very little difference between the ordinary temperature and the room temperature. In this case, the difference between the temperature of the temperature equalizing block 52 kept at ordinary temperature and the temperature of the ambient atmosphere at room temperature is small, consequently it is difficult to control the temperature. In addition, changes in the temperature of the ambient atmosphere surrounding the semiconductor package immediately changes the temperature of the surface of the semiconductor package. Accordingly, it is very difficult to stably maintain the temperature of the semiconductor package at an ordinary temperature near a room temperature.
As described above, in the related device for controlling the temperature of a semiconductor module used in the environmental temperature test, by placing the semiconductor module on the temperature equalizing block controlled at the test temperature, the temperature of the semiconductor module is caused to reach the test temperature. However, there is a problem that the temperature of the semiconductor module is difficult to be controlled precisely, since a temperature difference occurs due to heat resistance between the temperature equalizing block and the semiconductor module.
When the control temperature is near room temperature, it is difficult to control the temperature of the semiconductor module, since the difference between the temperatures of the semiconductor module and the temperature of the ambient atmosphere is small. In addition, there is another problem that a fluctuation in the room temperature directly leads to large change of the temperature of the semiconductor module.
It is an object of the present invention to provide a device and method for controlling temperature, which make it possible to precisely control the temperature of a semiconductor module to a predetermined temperature.
It is another object of the present invention to provide a device and method for controlling the temperature of a semiconductor module, which make it possible to precisely control the temperature of the semiconductor module near ordinary temperature and which are unaffected by changes in the temperature of ambient atmosphere.
FIG. 2 is a side view of an assembly of a first embodiment of the present invention, showing the structure of supporting units of a semiconductor module. FIG. 3 is a sectional view of the first embodiment of the present invention, showing a state in which the semiconductor module, mounted to a socket, is supported by the supporting units.
Referring to FIGS. 2 and 3, in a first structure of the present invention, a first heat transfer surface 25 of a first supporting unit 20 and a second heat transfer surface 31 of a second supporting unit 30 contact different portions, such as the top and bottom surfaces, of a semiconductor module 10, respectively. Through both of the heat transfer surfaces 25 and 31, heat is exchanged between the first and second supporting units 20 and 30 and the semiconductor module 10, respectively.
The second supporting unit 30 further includes a temperature sensor 34 and a heat insulating section 33. The heat insulating section 33 is provided near an area including the second heat transfer surface 31 and the temperature sensor 34, and limits heat flow to that from only the second heat transfer surface 31 with regard to heat flowing into and out of this area. This limiting operation is not limited to the case where, with regard to the flowing-in and flowing-out of heat of the area, heat flow from portions other than the second heat transfer surface is nearly blocked. For example, this operation may be more or less limited heat flow into and out of this area from the portions other than the second heat transfer surface.
In the first structure, the temperature of the first supporting unit 20 is cotrolled so that the temperature measured by the temperature sensor 34, which measures the temperature of the area of the second supporting unit 30 insulated by the heat insulating section 33, is equal to a predetermined temperature which is a control target temperature. Here, the temperature of the first supporting unit 20 is not controlled so that it equals a previously determined temperature. The temperature of the second supporting unit 30 measured by the temperature sensor 34 is controlled so that it equals the target temperature.
When the temperature of the first supporting unit 20 is lower than that of the second supporting unit 30, heat flows into the semiconductor module 10 from the second heat transfer surface 31 through a portion of the semiconductor module 10 that contacts the second heat transfer surface 31. From another portion of the semiconductor module 10, the heat flows into the first supporting unit 20 through the first heat transfer surface 25 that contacts this another portion. On the other hand, when the temperature of the first supporting unit 20 is higher than that of the second supporting unit 30, heat flows in the opposite direction. Therefore, based on the heat resistances between the first and second heat transfer surfaces 25 and 31 and the semiconductor module 10, a temperature difference occurs between the first and second supporting units 20 and 30 and the semiconductor module 10 in proportion to the amount of heat flow through these heat transfer surfaces 25 and 31.
In the above-described first structure of the present invention, the area of the second supporting unit 30, in which the temperature sensor 34 and the second heat transfer surface 31 are disposed, is shielded thermally by the heat insulating section 33. Therefore the amount of heat flowing into and out of this area is small. The amount of heat flowing through the second heat transfer surface 31 is equal to the sum of the amount of heat required to make the temperature of this area equal to the target temperature and the amount of heat flowing into and out of this area through the periphery of this area except the second heat transfer surface 31. In the structure, since the amount of heat flowing into and out of this area through the periphery of this area except the second heat transfer surface 31 is small, the amount of heat flowing through the second heat transfer surface 31 is small. As a result the difference between the temperature of the second supporting unit 30 (more exactly the area including therein the second heat transfer surface 31 and the temperature sensor 34) and the temperature of the semiconductor module 10 is small. Therefore, the temperature of the semiconductor module 10 can be made nearly equal to the temperature of the second supporting unit 30 with a slight temperature difference. The temperature of the second supporting unit 30 is measured by the temperature sensor 34 and is controlled based on the measurement result, and is, thus, maintained precisely at the predetermined temperature. Consequently, the temperature of the semiconductor module 10 is controlled so as to be almost equal to the predetermined temperature with a slight temperature difference.
When heat is generated from the inside of the semiconductor module 10, the generated heat raises the temperature of the semiconductor module 10 and then raises a temperature of a portion of the second supporting unit 30 near the second heat transfer surface 31. This temperature rise is immediately detected by the temperature sensor 34 disposed near the second heat transfer surface 31 and is corrected. This correction is achieved by increasing the amount of heat flowing into the first supporting unit 20 from the semiconductor module 10 through the first heat transfer surface 25 by lowering the temperature of the first supporting unit 20. Therefore, the generated heat in the semiconductor module 10 is absorbed mainly as a result of an increase or decrease in the temperature difference between the first heat transfer surface 25 and the semiconductor module 10, so that the amount of heat flowing through the second heat transfer surface 31 does not vary significantly. For this reason, the difference between the temperatures of the second supporting unit 30 and the semiconductor module 10 varies little, thereby making it possible to precisely control the temperature of the semiconductor module 10 that generates heat.
The area where heat is blocked may be limited to a small portion of the second supporting unit 30 so as to reduce the heat capacity of this area. By this limitation it is possible to sensitively detect a change of the temperature of the semiconductor module 10. In addition, the heat insulating section 33, provided at the second supporting unit 30, increases the heat resistance between the second supporting unit 30 and the external environment, such as indoor ambient atmosphere. Therefore, the change of the temperature of the external environment does not substantially influence on the controlling operation of the temperature of the semiconductor module 10.
FIG. 5 is a sectional view of an assembly of a second embodiment of the present invention, showing supporting units of a semiconductor module.
Referring to FIG. 5, a temperature regulator 36 for raising and lowering the temperature of a second supporting unit 30 may be provided in place of the heat insulating section 33 of the above-described first structure in the present invention. The temperature regulator 36 is driven so that the temperature of the second supporting unit 30 is maintained nearly at a control target temperature or becomes at least close to the control a target temperature. This driving operation may be performed to control the temperature of a portion of the second supporting unit 30 other than the area including the temperature sensor 34 at a previously determined temperature, or to generate or absorb heat in the second supporting unit 30 according to a predetermined sequence. In this structure, since the difference between the temperatures of the area including the temperature sensor 34 and portions near this area is small, the amount of heat flowing into and out of the area is small, thereby making it possible to provide similar advantages to those provided when the heat insulating section 33 is disposed.
Referring to FIG. 5, in a second structure of the present invention, similarly to the already mentioned first structure, a first heat transfer surface 25 disposed on a first supporting unit 20 and a second heat transfer surface 31 disposed on a second supporting unit 30 contact different portions of a semiconductor module 10, respectively, so that heat is exchanged between the supporting units 20 and 30 and the semiconductor module 10 through both of the heat transfer surfaces 25 and 31.
In the second structure, the temperatures of the first and second supporting units 20 and 30 are each controlled at different predetermined temperatures. Heat flows through the semiconductor module 10 based on the temperature difference between the first and second supporting units 20 and 30. During the temperature test, the temperatures of both of the supporting units 20 and 30 are maintained at certain temperatures so that the heat flow is steady. When the heat flow is steady, the amount of heat flowing through both of the heat transfer surfaces 25 and 31 is constant. Therefore, the difference between the temperatures of the semiconductor module 10 and both supporting units 20 and 30 does not change with time, and, thus, becomes constant. As a result, the temperature of the semiconductor module 10 is maintained at a constant temperature intermediate between those of the first and second supporting units 20 and 30. For the case where the predetermined temperatures of the supporting units 20 and 30 change in a quasi-steady manner in accordance with the temperature sequence, a similar argument can be made.
The temperature of the semiconductor module 10 in the second structure is determined by the temperatures of the first and second supporting units 20 and 30 and the heat resistances between the semiconductor module 10 and the first and second heat transfer surfaces 25 and 31. The heat resistances between the semiconductor module 10 and the first and second heat transfer surfaces 25 and 31 is constant after the semiconductor module 10 has been mounted to the supporting units 20 and 30, so that it does not change with the passage of time and with changes of the temperatures of the supporting units 20 and 30 with. Therefore, when the heat resistances of the two heat transfer surfaces 25 and 31 or the ratio between the heat resistances is previously known, it is possible to set the temperatures of the first and second supporting units 20 and 30 so that the temperature of the semiconductor module 10 is set at a predetermined temperature. In other words, the temperature of the semiconductor module 10 can be made exactly equal to the predetermined temperature. The heat resistances can be known by, for example, measuring the temperature of the semiconductor module 10, and comparing it with the temperatures of the supporting units 20 and 30.
The temperatures of the first and second supporting units 20 and 30 that can maintain the temperature of the semiconductor module 10 at the predetermined temperature are not limited to one value set. For example, the temperature of the semiconductor module 10 can be maintained at the predetermined temperature by making the temperature of one of the supporting units higher and that of the other supporting unit lower. Therefore, it is possible to control the temperature of the semiconductor module 10 to the predetermined temperature under the condition of large temperature difference existing between the first and second supporting units 20 and 30. By making the difference between the temperatures of the supporting units 20 and 30 large as mentioned above, the amount of heat flowing through the heat transfer surfaces 25 and 31 is made large, so that stability of the temperature control can be enhanced. When the predetermined temperature is close to room temperature, since the difference between room temperature and the temperatures of the supporting units 20 and 30 to be subjected to temperature control can be made large, the temperatures of the supporting units 20 and 30 is also stably controlled. When the amount of heat flowing through the heat transfer surfaces 25 and 31 is large, the temperature of the semiconductor module 10 is always precisely controlled to the predetermined temperature in accordance with the ratio between the heat resistances regardless of the temperature difference between the semiconductor module 10 and the heat transfer surfaces 25 and 31.
In the above-described second structure of the present invention, when the amount of heat generated in the semiconductor module 10 is constant, the temperature of the semiconductor module 10 can be exactly controlled to the predetermined temperature by considering that the temperature of the semiconductor module 10 increases by the corresponding rise in temperature of the semiconductor module 10 due to the heat generation. Even when the amount of generated heat changes (for example, even when the amount of generated heat depends upon the temperature of the semiconductor module 10), if the rise in temperature by the heat generation can be known, it is possible to know the exact temperature by correction. However, when the amount of generated heat changes, it is usually difficult to know the amount of rise in temperature. In such a case, the large temperature difference between the supporting units 20 and 30 increases the amount of heat flowing through the heat transfer surfaces 25 and 31, so that the ratio of the change of the heat flow amount due to the heat generation in the semiconductor module 10 is made small. As result, it is possible to reduce the influence of the heat generation in the semiconductor module.
A third structure of the present invention relates to a method of controlling temperature by heat exchange with a semiconductor module through a plurality of heat transfer surfaces. The method of controlling temperature relates to the above-described second structure of the present invention corresponds to the case where two heat transfer surfaces are used in the third structure.
In the third structure, the temperatures of the plurality of heat transfer surfaces are controlled at predetermined temperatures respectively, and the temperature of at least one of the plurality of heat transfer surfaces is controlled at a temperature that is different from the temperatures of the other heat transfer surfaces. Therefore, as in the description of the second structure of the present invention, temperature control can be carried out so that the temperature of the semiconductor module, which contacts these heat transfer surfaces, is equal to a predetermined temperature. The third structure provides operations and advantages that are substantially the same as those provided by the second structure of the invention, such as that stable temperature control is achieved, and that the effects of, for example, room temperature are small.
In the above-described first and second structures, the semiconductor module 10 may be interposed between the heat transfer surfaces 25 and 31 disposed so as to oppose each other. By interposing the semiconductor module 10, the heat transfer surfaces 25 and 31 can be pressed against the semiconductor module 10, so that heat resistances therebetween can be made small.
In the first and second structures, by using a specially constructed supporting unit and a socket, it is possible to control the temperature of the semiconductor module with the semiconductor module being mounted to the socket. Hereunder, a description of the supporting unit and the socket will be given.
With reference to FIGS. 4A and 4B, a socket 40 for mounting the semiconductor module 10 thereto has a through hole 42 formed in the center of a socket base 41. A head section 32 is provided so as to protrude from the supporting unit, with an end of the head section 32 being a heat transfer surface 31. The head section 32 is fitted through the through hole 42, so that the heat transfer surface 31 protrudes from the socket base 41. The protruding heat transfer surface 31 contacts the surface of the semiconductor module 10 mounted to the socket base 41. By using the supporting unit and the socket, the temperature controlling devices in accordance with the already described first and second structures of the present invention can be applied with the semiconductor module being mounted to the socket. The head section 32 that is fitted through the through hole 42 of the socket 40 may be provided in either of the first and second supporting units 20 and 30.
In a fourth structure of the present invention, a first unit for controlling the temperature of a semiconductor module and a second unit for measuring the temperature of the semiconductor module are disposed apart from each other as separate units. For the semiconductor module, a portion suitable for controlling temperature and a portion suitable for measuring temperature are sometimes different. In this structure, these portions can be separately thermally connected.
Since the inside of the semiconductor module is not homogeneous, even if an attempt is made to change the temperature of the semiconductor module by desired temperature, the rate of changes in temperature of the semiconductor module (changes in temperature per unit time) is sometimes different from the rate of changes in temperature of the first unit for controlling temperature. According to this structure, the temperature of the first unit for controlling temperature is not measured. The second unit that thermally contacts the semiconductor module separately of the first unit is used to measure the temperature of the semiconductor module, so that the rate of changes in temperature of the semiconductor package can be more precisely obtained than that when the temperature of the first unit is measured.